Effects of strength training with elastic band programme on fitness components in young female handball players: a randomized controlled trial

This study examined the effect of a 10-week programme of strength training with elastic band (STEB) on fitness components in young female handball players. Twenty-six young female handball players (aged 15.8 ± 0.2 years) from the same club participated in this study. They were randomly assigned between experimental (EG; n = 13) and control (CG; n = 13) groups. The EG performed the STEB, replacing some handball-specific drills in the regular handball training. The CG followed the regular handball training (i.e., mainly technical-tactical drills, small sided and simulated games, and injury prevention drills). Two-way analyses of variance were used to assess: handgrip; back extensor strength; medicine ball throw; 30 m sprint times; Modified Illinois change-of-direction (Illinois-MT); four jump tests: squat jump (SJ), countermovement jump (CMJ), countermovement jump with arm swing (CMJA) and five-jump test (5JT); static (Stork test) and dynamic balance (Y Balance Test); and repeated sprint T-test (RSTT). Results revealed significant gains in handgrip - right (p < 0.001, d = 1.75: large), handgrip - left (p < 0.001, d = 2.52: large), back extensor (p < 0.001, d = 2.01: large), and medicine ball throw (p = 0.002, d = 0.95: large) with EG compared to the CG. The EG also demonstrated greater improvement in sprint performance over 20 m (Δ = 10.6%, p = 0.001, d = 1.07: large) and 30 m (Δ = 7.2%, p < 0.0001, d = 1.56: large) compared to the CG. The EG showed better Illinois-MT (Δ = 5.6%, p = 0.034, d = 0.62: medium) compared to the CG. Further, EG posted significant improvements in the SJ (Δ = 17.3%, p = 0.048, d = 0.58: medium), CMJ (Δ = 17.7%, p = 0.017 d = 0.71: medium), and CMJA (Δ = 16.3%, p = 0.019, d = 0.69: medium) compared to the CG. Similarly, the EG exhibited significant improvement in RSTT best time [p = 0.025, d = 0.66 (medium)], RSTT mean time [p = 0.019, d = 0.69 (medium)] and RSTT total time [p = 0.019, d = 0.69 (medium)] compared to the CG. In conclusion, the 10-week STEB improved the physical abilities in young female handball players.

INTRODUCTION age = 15.7 ± 0.2 years; body mass = 64 ± 3 kg; height = 1.70 ± 0.04 m; % body fat = 25.3 ± 1.7; and maturity-offset = 3.3 ± 0.4 years) and a control group of players who maintained their standard in-season regimen (CG; n = 13; age = 15.8 ± 0.2 years; body mass = 64 ± 4 kg; height = 1.67 ± 0.04 m; % body fat = 26.6 ± 3.4 ; and maturity-offset = 3 ± 0.3 years). All participants were involved in five to six training sessions per week (90-120 min each session). The EG performed the elastic band training programme in replacement of some handball-specific drills so that the overall training volume was similar between groups.
The study was conducted to examine the effect of a 10-week STEB programme on fitness components in young female handball players. The training intervention was conducted during the in-season period in the year 2018-2019. In the week before the intervention, two, 90-min sessions were administered to allow player familiarization with the test procedures. Measurements were made in a fixed order over four days, immediately before and four days after the last strength training session. Subjects did not participate in any exhausting exercise 24 hours before testing, and no food or caffeine-containing drinks were taken for two hours before testing. A standardized warm-up (10-20 min of low-to moderate-intensity aerobic exercise and dynamic stretching) preceded all the tests. On the first test day, sprinting and change of direction abilities were measured. The second day was devoted to jumping and handgrip strength assessments. On the third day, anthropometric measurements were administered.
After that, back extensor strength and medicine ball throw tests were conducted. On the fourth day, the athletes completed the balance and repeated sprint tests.

Procedures and evaluation Day one 30 m sprint performance
Players started from a split stance standing position, with the front foot 0.2 m from the first photocell beam and sprinted for 30 m on command. Split times for 5, 10, 20 and 30 m distances were recorded for analysis [6].

Modified Illinois change-of-direction test (Illinois-MT)
Four cones formed the change-of-direction area for the modified Illinois test [14]. On command, players sprinted 5 m, turned and ran back to the starting line, then, swerving in and out of the 4 markers, completed two, 5 m sprints sprints. No advice was given as to the most effective technique, but players were instructed to complete the test as quickly as possible without cutting over markers. A trial is repeated if an athlete 'cuts' a marker while completing the task.
Three trials were allowed for the 30 m sprint performance and Illinois-MT (separated by 6-8 min of recovery) and the best time performances were noted using paired photocells (Microgate, Bolzano, Italy). et al. [7] revealed that 8-week eccentric hamstring training enhanced linear sprint time, change of direction, jump, and repeated sprint performance in young female handball players. In addition, Ignjatovic et al. [8] suggested that 12-week medicine ball training, when incorporated into a regular training session, demonstrated sportspecific training improvement in the upper body for young female handball players.
Recently, strength training using an elastic band (STEB) has been used as an alternative strength training scheme to improve physical performance in handball [9][10][11]. STEB is affordable, easy to use, portable, and provides a safe and effective progressive overload technique, applicable not only to athletes, but also to injured patients and sedentary people. In addition, STEB is a time-saving method for improving muscle strength and power of athletes during physical preparation [9]. In contrast, quantification of training load STEB is difficult to distinguish. A few studies have explored STEB in handball [9,10,12]. For example, Anderson et al. [10] demonstrated that STEB, incorporated into the regular handball training sessions, improved explosive lower-limb performance in young female handball players compared to handball training alone. Similarly, Mascarin et al. [13] observed enhancement in athletic performance, external rotator muscle strength, and balance after 6 weeks of STEB in young female handball players.
Given the potential of STEB in development of physical capabilities in handball, there seems to be a paucity in the literature investigating STEB in youth female handball athletes. Such undertaking can provide useful information in the application of STEB in the female youth handball setting. Thus, this study aimed to examine the effects of ten-week STEB on upper limb strength performances, sprint, change of direction, repeated change of direction, balance and jump performances in young female handball players. It is hypothesized that STEB improves upper limb power performances, sprint, change of direction, repeated change of direction and jump performances in young female handball players.

Ethical approval
All procedures were approved by the local ethical committee for the use of human participants of the Higher Institute of Sports and Physical Education of Ksar Saïd, Tunisia. The study was conducted in accordance with the latest version of the Declaration of Helsinki. Written informed parental consent (for those < 18 years) and participants' assent were obtained prior to the start of the study. All participants and their parents/legal representatives were fully informed about the experimental protocol and its potential risks and benefits.

Participants
Twenty-six young female handball players from the same club participated in this study. They were randomly assigned between an

Day two Vertical jump
Jump height was assessed using an infrared photocell mat connected to a digital computer (Optojump System; Microgate SARL) that measured contact and flight times and the height of jump with a precision of 1/1000 seconds [15]. Participants began the squat jump (SJ) at a knee angle of ~90°, avoiding any downward movement, and pushed upward, keeping their legs straight throughout.
The countermovement jump (CMJ) began from an upright position; a rapid downward movement to a knee angle of ~90° (again selfcontrolled, using a mirror) accompanied the beginning of the push-off.
During the countermovement jump with arm swing (CMJA), with hands used freely while jumping. Three trials were executed for each jump test, with one minute rest in between trials, and the highest jump from each test utilized in subsequent analyses.

Five-jump test (5JT)
The test was performed as previously described [6]. From an upright standing position with both feet flat on the ground, participants tried to cover as much distance as possible with 5 forward jumps, alternating left-and right-leg ground contacts. Participants were allowed 3 maximal trials, with 3 minutes of rest between efforts, and the best performance was used for analyses [6].

Handgrip strength test
The hand dynamometer (Takei, Tokyo, Japan) was held with the arm at a right angle and the elbows at the side of the body [16]. The instrument was adjusted so that its base rested on the first metacarpal and the handle rested on the middle of the 4 fingers. A maximal isometric effort was maintained for 5 seconds, without ancillary body movements. Two trials were administered for each hand, with 1 minute of rest between trials, and the highest readings were used in subsequent analyses.

Day three Anthropometry
Anthropometric measurements included height and sitting height

Back extensor strength
Maximal isometric back extensor strength was measured using a back extensor dynamometer (Takei) [19]. Participants stood on the dynamometer, with their feet shoulder width apart and gripped the handle bar positioned across the patellae. The chain length was adjusted so that initially the legs were held straight and the back was flexed to 30°, as guided by wall markings. Participants then stood upright without bending their knees, pulling upward as strongly as possible.

Medicine ball throw
The test was performed using 21.5-cm diameter, 3-kg rubber medicine balls (Tigar, Pirot, Serbia) powdered with magnesium carbonate.
A familiarization session included a brief description of the optimal technique [20]. The seated player grasped the medicine ball with both hands, and on a signal forcefully pushed the ball from the chest.
The score was measured from the front of the sitting line to the powder-marked spot where the ball landed. The recorded score (duration in seconds) was the best of three attempts [21].

Dynamic balance test
Dynamic balance was assessed on the dominant leg, using the Y-balance test [21]. Supine leg lengths were first determined from the anterior superior iliac spine to the most distal aspect of the me- All exercises were performed with the maximal effort level. The initial length of the elastic band was 120 cm for all exercises. The STEB was not added to the regular handball training but was immediately performed after the warm-up programme [10] in replacement of some low-intensity technical-tactical handball drills. The STEB replacement activity accounted for < 10% of the total handball-training load (competitive and friendly matches not accounted for). The CG subjects followed their regular handball training (i.e., mainly technical-tactical drills, small sided and simulated games, and injury prevention drills).
The overall handball training load was comparable between groups (using the Borg Rating of Perceived Exertion (RPE)). This is because they were following similar handball training routines consisting of 6 sessions per week with 90 to 120 min each.

Repeated sprint T-test (RSTT)
This test offers a reliable and valid measurement [22] of the ability to change directions rapidly, simulating a game with short, intense efforts, recovery periods and multi-directional displacements. Seven executions of the agility T-test were made, with subjects walking back slowly to the next start point during 25 s recovery intervals. The design of the STEB intervention was based on the players' previous training records and research results [9,10,12,13] (Table 1).

RESULTS
Test-retest reliability was above the established threshold and ranged from 0.742 to 0.992 according to the intra-class correlation coefficient and ranged from 2.0 to 54.1 according to the coefficient of variation (Table 2). Initial values showed no significant intergroup differences for any of the dependent variables. All data for both groups were significantly increased after the 10-week (Table 3 and Table 4 (Table 5) (Table 4). There were no significant differences in group × time interaction during static and dynamic balance performance between the EG and CG (Table 4).

DISCUSSION
This study examined the effects of a 10-week in-season STEB pro- with previous studies [9,26]. High levels of linear speed over short and medium (< 30-m) distances are important physical fitness attributes in handball [1] Enhancement in sprint performance after STEB can be attributed to transference capability of STEB to maximal running from increased knee extensor and flexor power production [26][27][28]. In addition, the amelioration in maximal speed from STEB may be influenced by neural adaptations because less hypertrophy occurs after training with elastic bands [29]. Secondly, sprint ability in 5 m and 10 m were not affected by STEB. Initial acceleration (over 5 and 10 m) has proven more difficult to enhance than maximal velocity, probably due to the smaller margin for improvement and various mechanical forces involved [6]. The lack of improvement in the acceleration phase after STEB in this study contrasts with the study by Aloui et al. [9]. The discrepancy in results could be explained properties [26]. In this study, STEB exhibited various characteristics in change of direction, pertaining to the repeated agility task. Repeated high-intensity agility is dependent on neuromuscular (e.g., neural drive and motor-unit activation) and metabolic factors (e.g., oxidative capacity, creatine phosphate recovery and H+ buffering) [33]. velocity factor of the power output more than the force factor for the lower limbs. This is supported by the velocity data, which showed an increased between-period difference in velocity in the vertical parameters in this study can be linked to an increased rate of force development from greater motor recruitment, [35,36] tendon stiffness, [37] or fascicle length [38,39].
This study has some limitations that need to be acknowledged.

Acknowledgments
The authors would like to thank the participants for their participation and commitment to the study. The authors declare that the experiments comply with the current laws of Tunisia, the country in which the study was performed. No external funding was received for this work.

Competing interests
The authors declare that they have no competing interests.
jump performance [9]. The mechanism responsible for this effect has been attributed mainly to neural adaptations such as an increased nerve conduction velocity, maximization of the electromyogram, improved intermuscular coordination, an enhanced motor unit recruitment strategy, and increased excitability of the Hoffman reflex (H-reflex), as well as changes in muscle size and architecture, in the mechanical characteristics of the muscle-tendon complex, and changes in single-fibre mechanics [29]. The SJ, CMJ, and CMJA findings agree with the results reported by Anderson et al. [10].
However, the SJ and CMJ results in this study contrasted with the findings of Aloui et al. [9], which demonstrated no significant changes in SJ and CMJ indices after 8-week STEB in elite junior male handball players. Discordant outcomes from the previous study may be related to methodological differences. Another finding in this study was the non-significant difference in 5JT. The STEB may not be suf- In another study by Mascarin et al. [13], STEB developed muscular strength of external rotator muscles and muscular balance in female youth handball players. The enhancement of upper limb performance